Although a number of clinicopathologic studies of active infective endocarditis have been reported, none have focused on patients studied at necropsy with active infective endocarditis confined to the mitral valve. This study examined the clinical and morphologic features in 63 patients with infected vegetations limited to the mitral valve. The following conclusions are drawn from the study of these patients: infection is more common in men than in women; and in previously normal valves than in previously abnormal valves; a predisposing factor is frequently present; vegetations do not cause or worsen valvular dysfunction; and endocarditis is commonly part of a generalized or systemic infection.